The present invention generally concerns a seat such as a working seat, for example an office chair or a vehicle seat.
In a seat as disclosed in European patent No. 0 022 933, the seat comprises a seat frame structure comprising a seat portion carrier and a backrest portion carrier with the backrest portion carrier of a generally L-shaped configuration in side view. One limb of the L-shaped backrest carrier, which is disposed substantially horizontally, extends under the seat portion carrier and is pivotably connected thereto, at the underside thereof, by means of a pivot shaft or spindle. The angle of inclination of the backrest can be adjusted, relative to the seat portion, by means of a gas spring which is operatively disposed between the base assembly of the seat and the limb of the L-shaped backrest portion carrier which engages under the seat portion carrier. The gas spring has to be operated by means of a suitable lever, for the purposes of adjusting the angle of inclination of the backrest portion.
In another form of seat in which the backrest portion carrier is also pivotable relative to the seat portion carrier for adjusting the angle of inclination of the former, the backrest portion carrier is supported by spring means so that the angle of inclination of the backrest portion adapts itself to the respective seating position in the seat. Although such a seat has the advantage that there is no need for any manual actuating operation for the purposes of adjusting the angle of inclination of the backrest portion, it does however suffer from the disadvantage that the backrest portion does not offer a rigid support to the occupant of the seat. Because the backrest portion has a tendency to yield to a force applied thereto, as for example when the occupant of the seat leans back and applies considerable weight to the backrest portion, so that the backrest portion does not firmly support the back of the occupant, the seat affords a `spongey` feel to the occupant, and a resulting impression of insecurity.
In yet another form of seat or chair having an adjustable backrest portion such as seats for use in rail vehicles, the backrest portion carrier is pivotable relative to the seat portion or squab carrier about a pivot axis which is disposed at the rearward end of the seat portion carrier, so that the backrest portion pivots relative to the seat portion in the manner of a folding knife. In that case the backrest portion carrier is not of the L-shaped configuration in side view as referred to above, but in essence only consists of a single limb, thus defining a generally planar frame construction. The seat portion carrier and the backrest portion carrier are guided in mounting rails in such a way that, upon a forward movement of the seat carrier portion, the backrest carrier portion is tilted backwards towards a position in which it extends horizontally, until the seat forms a couch arrangement in a fully reclining position. In that operation, the upper end of the backrest portion carrier moves vertically downwardly so that at the end of the reclining movement the seat portion has been moved forwardly by the length of the backrest carrier. A travel seat of that nature is to be found in German patent No. 2 054 817.
A seat as described in the foregoing paragraph is basically not suitable for use as a working seat or chair, for example in the form of an office chair, because the forward movement of the seat portion carrier which is necessary to provide a given angle of inclination of the backrest portion is excessive. In that seat, inclining of the backrest portion and thus the back of the occupant of the seat is achieved solely by the occupant sliding forward, together with the seat portion, by a suitably long distance. If that design principle were to be applied to a seat such as an office chair, the result would be that the occupant of the seat would have to push the office chair backwards by a correspondingly long distance in order not to alter the distance between the occupant of the seat and a surface such as a desk or working table at which that person was seated. Furthermore, the chair would have to be supported on the ground or floor by means of a support base assembly of very substantial dimensions in a horizontal direction so that, when the backrest portion was set into a fairly substantial angle of inclination, the chair would not become unstable on its base assembly by virtue of the long horizontal distance by which the centre of gravity of the seating configuration would be displaced relative to the base assembly.